A resolver on an IPv6-only end-system should not query for A (IPv4) records. These are useless to the system. mirrors.kernel.org has an AAAA (IPv6) record. The installer needs to send a query for the AAAA record. For some reason, it is not doing so. I could hazard a guess that the developers did not test an installation with the IPv4 stack disabled. I'd like to hear from them before publishing my findings.

yes. i know installer not send query for AAAA record.
but, i test ipv6 only dns server at 2009, if the remote dns server is dual-stack and the client(local ipv6 dns server) is ipv6 only, you can't get any ipv6 record.

I'm having difficulty parsing your statements. It sounds as though you are suggesting that dual-stack DNS servers won't return AAAA records over IPv6 transport. If this were true, there would be a lot of IPv6-only end stations that would be useless right now.